Rainfall

April 2011 rainfall was above to very much above average over much of the Kimberley,
as well as in parts of the west Pilbara and Southwest districts. Wyndham, Lake
Argyle Resort and Dampier Downs in the Kimberley observed their wettest April
on record, mainly due to heavy monsoonal rainfall during the first part of the
month. In contrast, much of the remainder of the southern half of the state
observed below average rainfall, with areas of very much below average in the
eastern Interior and western Gascoyne (see April 2011 rainfall totals
& deciles).

When averaged across the state, rainfall during April 2011 was above average;
while the Lower Southwest (southwest of a line from Jurien Bay to Bremer Bay) observed near average April rainfall.

Very heavy rainfall in the north Kimberley, due to a tropical low near the
north Kimberley coast resulted in Wyndham and Mount Barnett observing their
wettest April days on record on the 4th and 5th respectively. The wettest day
in April 2011 also occurred during this event with Mount Hart Station observing
206.0 mm, which is their third wettest day on record behind the 338.0 mm observed
on 9 April 1995 and the 259.1 mm observed on 12 February 1974. A low off the
Pilbara coast resulted in heavy rainfall over the east Pilbara where Telfer
observed its wettest April day on record on the 8th. A middle level cloud band
brought heavy rainfall to the west Pilbara, with Glen Florrie Station in the
inland west Pilbara observing 125.0 mm in the 24 hours to 9am on the 10th, their
wettest April day on record. Several cold fronts crossed the southwest of WA
over the Easter weekend, with daily totals in southern parts of the Southwest
Land Division mostly in the 10 to 20 mm range with isolated heavier falls.

The 2010/11 northern wet season has been particularly wet in northern parts
of Western Australia (see table below). Very warm sea surface temperatures combined
with an active monsoon trough that was present across northern Australia for
much of the wet season resulted in record rainfall at a number of sites in the
Kimberley. Heavy rainfall was also observed over the summer months in the Gascoyne
and far northern Southwest Land Division resulting in several flooding events
and record rainfall. Please refer to the Monthly
Weather Review for information on specific events.

Maximum temperature

April 2011 maximum temperature was above to very much above average in western
and southern parts of WA where Geraldton, Kalbarri and Esperance observed their
hottest April on record. In contrast, below to very much below average mean
maxima were observed in the northeast of WA, with Warmun, Wyndham and Troughton
Island observing their coolest April on record (see April 2011 mean maximum
temperature decile
& anomaly
maps)

When averaged across the state as a whole, mean maximum temperature during
April 2011 was near average; however, the Lower Southwest (southwest of a line
from Jurien Bay to Bremer Bay) observed its fourth hottest April on record (comparable
records commenced in 1950).

A cool day of just 16.2 °C was observed at Wiluna in the far northern Goldfields
on the 29th, which is their coolest April day in 52 years of record.

The Lower Southwest has experienced its hottest January to April on record
in terms of mean maximum temperature (comparable records commenced in 1950)
due an above average January, an above average February, 3rd hottest March and
an above average April.

Minimum temperature

The pattern of mean minimum temperature during April 2011 was similar to the
maximum temperature pattern, with above to very much above average overnight
temperature in western parts of WA, and below to very much below average in
the northeast of the state. (see April 2011 minimum temperature decile
& anomaly
maps). Wyndham in the east Kimberley observed their coolest April on record
with a mean minima of 15.9 °C during April 2011; while Hyden in the Great
Southern observed its warmest with 13.8 °C.

When averaged across the state as a whole, mean minimum temperature during
April 2011 was near average; however, the Lower Southwest (southwest of a line
from Jurien Bay to Bremer Bay) observed above average mean minima, with its
fourteenth warmest April on record (comparable records commenced in 1950).

A warm night was experienced in the Southwest on the 6th, with Cape Leeuwin
observing 21.6 °C, their warmest April night in 105 years of record.

The Lower Southwest has experienced its hottest January to April on record
in terms of mean minimum temperature (comparable records commenced in 1950)
due the 3rd warmest January, equal warmest February, 4th warmest March and an
above average April.

Notes

A Monthly Climate Summary is prepared to list the main features of the weather in Western Australia using the most timely and accurate information available on the date of publication; it will generally not be updated. Later information, including data that has had greater opportunity for quality control, will be presented in the Monthly Weather Review, usually published in the fourth week of the month.

This statement has been prepared based on information available at
11 am on Monday 2 May 2011.
Some checks have been made on the data, but it is possible that results will change
as new information becomes available.

Averages are long-term means based on observations from all available
years of record, which vary widely from site to site. They are not shown for
sites with less than 10 years of record.
The median
is sometimes more representative than the
mean
of long-term average rain.

The Rank indicates how rainfall this time compares with the climate record for the site,
based on the
decile ranking
(very low rainfall is in decile 1, low in decile 2 or 3,
average in decile 4 to 7, high in decile 8 or 9
and very high is in decile 10).
The Fraction of average shows how much rain has fallen this time as a
percentage of the long-term mean.

Records in this summary are based on sites with at least 30 years of data.

For PDF files of Perth Metro climate statistics for other months, please click
here
for extremes and
here
for averages.